"I don't see what's inherently wrong about hierarchy"
Then you aren't an anarchist. Anarchism literally means, 'without hierarchy'. You can't support one person effectively owning another person, having the right to boss them around, and be an anarchist. That isn't how it works.
A non-capitalist market would be mutualism. It hasn't happened yet because we haven't had a successful anarchist revolution. If I were a reactionary (for example, an 'an'-cap), I would be bound by precedent. I am not.
Iceland was a Scandinavian nation. They kept slaves. It's not that hard to find out.
Actually, I CAN deny the success of capitalism in making people of all classes vastly more wealthy. That's why we have an underclass. Capitalism isn't making them vastly more wealthy, because they are dispossessed and unemployed. Often, you're poor even if you DO work. And, although everyone is contributing (though the workers are the ones doing all the actual labor), the ones who own and invest seem to be the ones reaping most of the benefits of everyone else's labor. Now, I never claimed the capitalist did nothing. I claimed that he exploited the workers, and that this exploitation was more exploitative than the results of mutualism. Your defense of capitalists reads like a chicago school textbook, with the same classist, asinine assumptions that the capitalist class is some sort of special club made up all the motivated, strappy workers who boldly invested and steered their business to success. The truth is, most of the wealthiest people are the children of wealthy people, born into ownership. Many contribute literally nothing, not even their 'executive leadership' (actually, most companies hire someone else to do this, so quite a few capitalists contribute literally nothing). You need to pull the wool from your eyes and look at the real world.
As for mutualism, it is only theft under your view of property. Under the view of property used by mutualists and all other types of anarchist, your view of property is systemic theft of a worse degree, so we'd much prefer our property system. And, since our property systems can't coexist, and since your property system entails hierarchy, we as anarchists condemn your property system.